Numerous processes are within the purview of those skilled in the art for the preparation of toners. Emulsion aggregation (EA) is one such method. Emulsion aggregation toners may be used in forming print and/or xerographic images. Emulsion aggregation techniques may involve the formation of an emulsion latex of the resin particles, by heating the monomers, using a batch or semi-continuous emulsion polymerization, as disclosed in, for example, U.S. Pat. No. 5,853,943, the disclosure of which is hereby incorporated by reference in its entirety. Other examples of emulsion/aggregation/coalescing processes for the preparation of toners are illustrated in U.S. Pat. Nos. 5,902,710; 5,910,387; 5,916,725; 5,919,595; 5,925,488, 5,977,210, 5,994,020, and U.S. Patent Application Publication No. 2008/0107989, the disclosures of each of which are hereby incorporated by reference in their entirety.
Polyester toners exhibiting low melt properties have been prepared utilizing amorphous and crystalline polyester resins as illustrated, for example, in U.S. Patent Application Publication No. 2008/0153027, the disclosure of which is hereby incorporated by reference in its entirety.
To make polyester toners, resins utilized may be emulsified into an aqueous dispersion or emulsion. Two processes are often used to emulsify the polyester resins. The first method, phase inversion emulsification (PIE), utilizes ammonium hydroxide (10 wt % NH3 solution) as a neutralizing agent to react with the acid end groups on the polyester resins to form anionic groups. These anionic groups drive the formation of the emulsion, stabilize the emulsion particles in the aqueous phase and may be important in controlling the final emulsion particle size. However, ammonium hydroxide is a volatile solution of ammonia in water in which the vapors readily escape from the solution, causing the concentration of the basic solution to constantly change, thus constant measures need to be taken to ensure the correct concentration is used during the PIE process. In addition, exposure to ammonium hydroxide and its vapors can cause unsafe health conditions that can lead to chemical sensitivities for all operators when dealing with this process. Thus, extra precautions should be taken to protect operators from the caustic solution and the ammonia gas.
The second method includes a solvent-free emulsification process, formed in either a batch or extrusion process through addition of sodium hydroxide (NaOH) as a neutralizing agent for preparation of the emulsions, including a surfactant solution, water, and a thermally softened resin as illustrated, for example, in U.S. Patent Application Publication Nos. 2009/0208864 and 2009/0246680, the disclosures of each of which are hereby incorporated by reference in their entirety. However, NaOH is a strong base and nucleophile which leads to the degradation of the polyester resins. Thus tight constraints are needed to ensure this degradation does not occur.
Thus, these solventless latex emulsions have also been formed utilizing secondary amines, such as piperazine, as a neutralizing agent as illustrated, for example, in U.S. patent application Ser. No. 12/485,415, the disclosure of which is hereby incorporated by reference in its entirety, to replace the more volatile hydroxide bases conventionally utilized in these processes. Secondary amines, unlike NaOH, are miscible in the polyester resin, have a melting point of about 106° C., and can therefore act as a neutralizing agent directly in the melted resin without the need for water.
However, solventless processes can be less effective in creating resin emulsions from high molecular weight polyester resins.
Improved methods for producing toners, having optimal process conditions and less hazardous materials, remain desirable. Such processes may reduce production costs for such toners and may be environmentally friendly.